Electromagnetically actuated exposure control mechanism

ABSTRACT

An exposure control mechanism of a variety having two blades driven from a reciprocally pivotable walking beam. The mechanism is actuated by selectively energizing and de-energizing a solenoid having a plunger retractable within an excitation winding upon energization of the latter. The plunger is biased outwardly by a compression type opening spring providing an abuttable contact between the plunger tip and walking beam. A closing spring attached to the walking beam serves to bias the blades of the mechanism to move in a closing direction. Because the opening spring has a higher force value characteristic than the closing spring, the mechanism normally defines an open shutter condition. When the solenoid is energized, the plunger moves to compress the opening spring and negate its abuttable contact with the walking beam to permit the shutter to be closed under the isolated drive of the closing spring.

ite States Patent 1 Douglas Nov. 6, 973

ELECTROMAGNETICALLY ACTUATED EXPOSURE CONTROL MECHANISM [75] Inventor:Lawrence M. Douglas, South Easton,

Mass.

[73] Assignee: Polaroid Corporation, Cambridge,

Mass.

[22] Filed: Apr. 21, 1972 [21] App]. No.: 245,801

[52] U.S. Cl 95/53 EB, 95/56, 95/62 [51] int. Cl. G03b 9/42 [58] Fieldof Search 95/10 CE, 53 EB,- 95/11 SR, 56,59, 53 EA, 53 E, 62, 64 B [56]References Cited UNlTED STATES PATENTS 3,661,066 5/1972 Ettischer 95/53EB ABSTRACT An exposure control mechanism of a variety having two bladesdriven from a reciprocally pivotable walking beam. The mechanism isactuated by selectively energizing and de-energizing a solenoid having aplunger retractable within an excitation winding upon energization ofthe latter. The plunger is biased outwardly by a compression typeopening spring providing an abuttable contact between the plunger tipand walking beam. A closing spring attached to the walking beam servesto bias the blades of the mechanism to move in a closing direction.Because the opening spring has a higher force value characteristic thanthe closing spring, the mechanism normally defines an open shuttercondition. When the solenoid is energized, the plunger moves to compressthe opening spring and negate its abuttable contact with the walkingbeam to permit the shutter to be closed under the isolated drive of theclosing spring.

26 Claims, 5 Drawing Figures I ELECTROMAGNETICALLY ACTUATED EXPOSURECONTROL MECHANISM BACKGROUND OF THE INVENTION An exposure control systemembodying a mechanism providing two parameter exposure control within aninvolved reflex photographic cycle is described in a US. Pat. by V. K.Eloranta, entitled Exposure Control System, No. 3,641,889. Uniquelydesigned to be packaged within the very limited confines of the exposurecontrol housing of a thin, compact camera, the exposure control systemis characterized in the use of a tractive electromagnetic device, suchas a solenoid, which is energized for the purpose of closing exposuremechanism blades. In a preferred embodiment of the system, two suchexposure mechanism blades are provided which operate simultaneously andin synchronism through connection with a reciprocating walking beam"type drive assembly. The latter assembly, in turn, is actuated by thenoted solenoid in cooperation with a spring drive.

A technique for improving the dynamic performance of the above notedsolenoid actuated exposure control system is described and claimed in acopending application for US. Pat. by C. C. Petersen, entitledDynamically Compensated Exposure Control System, Ser. No. 245,800, filedof even date herewith an assigned in common herewith. With thiscompensation technique, the dynamic performance or motion imparted inconsequence of energization of the drive solenoid is isolated fromexposure mechanism blade movement. For instance, both opening andclosing movement of the blades of the exposure mechanism are provided bysprings evidencing consistently repeatable force values or ratecharacteristics. Through an arrangement by which the solenoid is drivenonly against substantially mass isolated force values exhibited by oneof the springs, the exposure control system is capable of operating withrequisite statistical consistency even though energy input variationsare encountered at its power supply.

The above noted dynamic corrections necessarily add to the complexity ofthe mechanism of the subject exposure control systems, and, as aconsequence, add to their cost and bulk. To incorporate a desirablycompensated system within the very limited confines of an exposurecontrol housing of a thin, compact camera, a mechanism which carries outall of the necessary functions of the system while remaining both simpleand highly compact is needed. For instance, such a mechanism should notrequire any addition to the size of the exposure control housing withinwhich it is situated;

Of particular importance, where such compensated exposure mechanisms arerequiredto be incorporated within popularly priced cameras, fabricationthereof must be available under high volume production procedures. Forinstance, the mechanisms must utilize a'very minimal number of parts.Further, the exposure mechanism assemblies comprising these partsmust-be fabricable using automatic assembly machines and the like.

Preferably, the parts must be directly insertable within a camerahousing, no multidirectional manipulation thereof being acceptable underpreferred manufacturing conditions.

SUMMARY OF THE INVENTION The instant invention provides an exposurecontrol mechanism of a variety actuated by selective energization of asolenoid and which is characterized in requiring a small number ofeasily assembled components to remain dynamically compensated. Dynamiccompensation of the mechanism is provided in a manner permitting its usewithin the very limited confines of the exposure control housing withina thin, compact photographic camera of a size suited for carrying in thepocket of a garment.

Desirable simplicity as well as compactness of the exposure mechanism isavailed through an assembly wherein the tractive electromagnetic deviceor solenoid thereof incorporates a plunger which is spring biased awayfrom its positions of enhanced flux linkage. One end of the plunger ofthe solenoid is configured to provide a striker surface which, under thenoted spring bias, is movable into abuttable contact with a light valveor shutter type exposure mechanism. The light valve arrangement isbiased for movement to block an exposure aperture, however, when thenoted abuttable contact is made, and the drive solenoid is de-energized,the light valve is driven toward orientations unblocking the exposureaperture. With the above-described arrangement, the influence of openingdrive upon the light valve is negated while the valve is being driven toan aperture blocking orientation. As a consequence, desirably consistentdynamic closing performance is provided by the mechanism.

In a preferred arrangement, the bias exerted upon the solenoid plungeris provided by a compression spring constrained between an outer portionof the plunger and a mounting assembly of the solenoid. Further, suchcompression springs advantageously may be selected having a relativelyhigh spring index, for instance over about 20, to lessen the powerdemands imposed upon a solenoid used within the exposure mechanism.

Another feature and object of the invention is to provide an exposurecontrol mechanism of a variety including shutter-aperture blades movablebetween terminal positions in consequence of their connection with areciprocally movable actuator or drive assembly resembling a walkingbeam. This drive assembly is movable in consequence of the actuation ofa solenoid or the like. The solenoid is formed having an excitationwinding'as well as a plunger and'housing arrangement, the plunger beingarranged to be retracted within the excitation winding upon energizationof the solenoid. An opening spring is arranged for cooperation with theplunger in a manner urging the outwardly disposed tip thereof intocontact or abutment with the actuator or walking beam arrangement.Theactuator or walking beam, itself, is biased for movement in a mannerwherein the blades of the mechanism are urged to move in synchronism toblock an exposure aperture. Preferably, this bias is provided by aclosing spring having a. relatively flat rate loading characteristic.The noted exposure aperture is unblocked by the procedure ofde-energizing'the excitation winding of the solenoid. With suchde-energization, the opening spring urges the tip of the solenoidplunger into contact with the actuator to drive the blades toward openaperture'positions against the mass-accellerative characteristics of theblade as well as the bias exerted by the closing spring.

To terminate an exposure, the excitation winding of the solenoid isenergized to retract the noted plunger against the bias of the openingspring. Movement of the actuator by the closing spring, however, isisolated from opening spring and solenoid activity inasmuch as theearlier abutting contact is negated. Through this arrangement,consistant and repeatable opening and closing dynamic characteristicsadvantageously are realized with the mechanism.

Another feature and object of the invention is to provide a mechanism asabove-described which is formed of significantly few and simplecomponent parts such that the entire mechanism may be fabricated usinghigh volume automatic assembly techniques. In a preferred arrangement,the noted opening spring is provided as a compression spring constrainedbetween a mounting arrangement for the solenoid and an outer portion ofthe plunger. Representing a subassembly, the solenoid and opening springare simply directly insertable within the housing of the exposurecontrol mechanism. Additionally, the actuator or walking beam assembly.may be of relatively simple design suited for facile attachment withinthe noted exposure control housing.

Another feature and object of the invention is to provide a mechanism asabove described wherein the opening spring is configured as acompression spring and constrained between a solenoid mountingarrangement and its reciprocally movable plunger, such spring beingselected as a compression spring having a relatively high spring index.Such a high index, for instance above about twenty, permits a relativelyflat rate characteristic serving to economize upon the powercharacteristics required of the solenoid structure. Further, the notedclosing spring preferably is selected having a relatively flat ratecharacteristic in the interest of solenoid power economy. Theserelatively flat rate spring characteristics cooperate to permit lowersolenoid power levels, a feature of particular importance where thin,compact camera designs are involved.

As another feature and object of the invention, means may beincorporated for adjusting the preloading characteristics of the notedclosing spring to provide for calibration of the entire mechanismagainst a predetermined dynamic standard. The latter calibrationenhances the availability of the mechanism to camera designs suited tobe manufactured for sale at popular prices.

Other objects of the invention will in part be obvious and will, inpart, appear hereinafter.

The invention accordingly, comprises the mechanism and apparatuspossessing the construction, combination of elements and arrangement ofparts which is exemplified in the following detailed disclosure. For afuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is'a front elevational view ofan exposure control housing incorporating the exposure control mechanismof the instant invention and showing an orientation of componentsproviding for the full unblocking of an exposure aperture;

FIG. 2 is a top partial view of the exposure mechanism of FIG. 1;

FIG.'3 is a front elevational view of the exposure con trol housing ofFIG. 1 showing the exposure mechanism components thereof as they areoriented to provide for the complete blocking of an exposure aperture;

FIG. 4 is a front elevational view of the exposure control housing ofFIG. 1 showing an orientation of exposure mechanism components as theydefine an aperture opening of intermediate exposure value; and

FIG. 5 is a graph incorporating representative spring rate curves forthe mechanism of the invention.

DETAILED DESCRIPTION The mechanism of the instant invention isparticularly suited for use within the exposure control housing of avery thin and compact camera suited for carrying in the pocket of agarment. Such a camera has been described in US. Pat. No. 3,7l4,879. Thenoted exposure control housing must be foldable into a nestedorientation with the other components of the thin camera to achieverequisite compactness and, accordingly, the space available for all thecomponents of a fully automated exposure system is extremely limited.Such components include focusing gears, trim adjustment mechanisms,follow-focus actuating and trim systems, lens mountings and the like. Amore detailed illustration of such components as they are fashioned foruse within the exposure control housing is provided in a copendingapplication for US. Pat. by L. G. Douglas, Ser. No. 168,671, entitledApparatus and System for Flash Photography filed Aug. 3, 1971 andassigned in common herewith. In the interest of facilitating thedescription of the mechanism of the instant invention, certain of theseabove-cataloged components are deleted from the drawings and descriptionto follow.

Referring to FIGS. 1 and 2, the noted thin and compact exposure controlhousing is illustrated generally at 10. The principal supportingstructure for housing 10 is present as a rear casting 12 which isselectively machined to support the components of the mechanism.Surrounding the front and top of casting 12 is a front cover 14 which isstructured at 16 to support a packaged flash lamp array and relatedcomponents and which includes openings (not shown) through whichprotrude manually adjustable trim and'focus wheels, the boundries ofwhich are shown respectively at 18 and 20. I

Centrally disposed within the back wall of casting 12 is an annularexposure opening 22, the periphery of which substantially defines thelargest available aperture width for the mechanism. The light valveassembly within housing 10 is present as a dual bladed exposure controlarrangement including blades 24 and 26 as well as an interconnectingactuator 28, the operation of which resembles that of a walking beam.Blades 24 and 26 are slidably mounted within a bracket 30 fixed, inturn, to rear casting 12. Bracket 30 additionally serves as a supportfor an externally threaded lens housing or bezel, the periphery of whichis illustrated by circular outline 32. Connection between bezel 32 andfocus wheel 20 is provided by an idler gear shown in phantom at 34.

Blades 24 and 26, respectively, are configured having teardrop-shapedopenings 36 and 38 formed therewithin. Openings 36 and 38 are positionedwithin respective blades 24 and 26 in a reversed sense such that, asthey symmetrically overlap, they combine to form a symmetricallyconfigured aperture opening across exposure opening 22.

The symmetry of the aperture openings defined by blades 24 and 26 isrealized as a consequence of their connection with reciprocally movableactuator or walking beam 28. Walking beam 28 is seen to be journalled atabout its midpoint for rotation about a stud 40, fixed to and extendinginwardly from the forward face 42 (FIG. 2) of a U-shaped bracket 44.Spacing of beam 28 from face 42 is provided by an integrally formedcollar 76 and associated washer 78. Elongate slots as at 50 and 52 areformed in the outward portions of walking beam 28 for the purpose ofproviding connection with pins 54 and 56 fixed to and extending,respectively, from blades 24 and 26.- Thus interconnected, the blades 24and 26 may move simultaneously and in correspondence with each other todefine symmetrically configured aperture openings of progressivelyvarying values over exposure opening 22. Elongate slots 50 and 52 servethe function of accommodatingfor the horizontally restricted movement ofthe blades 24 and 26 along cords extending through the locus of rotationof the tip of beam 28.

Blades 24 and 26 also are configured having elongate portions,respectively shown at 58 and 60, which extend through a light detectingstation, shown generally at 62. Elongate portions 58 and 60,respectively, are formed incorporating secondary openings 64 and 66which are configured in light regulating correspondence with theconfigurations of respective openings 36 and 38. Secondary openings 64and 66 are oriented upon respective elongate portions 58 and 60 in amanner wherein they overlap in a symmetrical and mutually reversed senseto define a secondary aperture opening 68 within light detecting station62. Opening 68, in turn, is located intermediate the photosensingelements of an exposure control circuit and an entrance optical assemblyincluding a lens, outlined at 70, and a supporting bracket therefor,shown at 72. Bracket 72 is connected by rivets as at 74 to rear casting12.

The instantaneous aperture openings defined at 68 are derived insynchronism with those present at exposure opening 22. Accordingly, theselective attenuation of scene light entering detecting station 62serves to modulate a resultant signal to providean instantaneousaperture value input to the exposure control circuit of the system. Suchinput permits the system to provide a two parameter exposure control.

To operate in conjunction with the program of a reflex photographiccycle, blades 24 and 26 must be actuated in a manner whereby openings 36and 38 define an aperture of maximum available width prior to thecommencement of such cycle. This normally open shutter condition, asshown in FIG. 1, facilitates viewing and focusing procedures. Whenoperated to define an interval of exposure, exposure mechanism blades 24and 26 are driven into an orientation wherein they fully block exposureopening 22. This closed orientation is shown in FIG. 3. An exposureinterval is defined by moving the blades in synchronism to graduallyopen and define progressively varying aperture values until apredetermined exposure value is reached. When this value is reached, forinstance, as illustrated in FIG. 4, a tractive electromagnetic device inthe form of a solenoid such as that depicted generally at 80 isenergized to terminate the exposure interval by actuating the lightvalve arrangement including blades 24'and 26 to cause their return tothe closed orientationillustrated in FIG. 3.

Consistent dynamic performance of the mechanism in driving blades 24 and26 between open orientations and a closed terminal position is realizedthrough an arrangement wherein solenoid is coupled to be operatedsubstantially only against the force of a spring bias, while movement ofblades 24 and 26 with their attendant mass-accelerative as well asfrictional characteristics is supplied only from springs.

Solenoid 80 is formed having an excitation winding 82 which is woundabout a cylindrically-shaped hollow bobbin, the flange portions of whichare shown at 84. Bobbin 84, in turn, is connected to a U-shaped frame orsupport fixed to the bottom portion of rear casting Internally disposedwithin excitation winding 82 and bobbin 84 is a cylindrically-shapedplunger or movable armature 88. Plunger 88 is configured to slidablyretract within bobbin 86 and winding 84 upon energization of the latterand is formed having an externally disposed tip including a strikersurface 90 and an annular flange portion 92. Plunger 88 is biased tomove from its retracted position by a compression spring 94 mountedcoaxially thereabout and constrained between frame or support 86 andflange portion 92. An examination of compression spring 94 reveals thatit is formed of a multitude of coils of a wire having a diameter ofrelatively small value when compared with the mean diameter of thecylindrically-s'haped spring itself. This spring structure is onederiving a relatively high spring index representing the ratio of springcoil diameter to the diameter of the wire forming those coils. In thepresent embodiment, it is preferred that compression spring 94 beselected having a spring index of value higher than about 20. I

Spring 94 serves to urge plunger 88 away from its retracted positionwithin excitation winding 82 in a manner urging its striker surface 90into abuttable contact with the striking surface of a pin 96 which isfixed to and extending from the lower leg of walking beam 28. Thusconfigured, when solenoid 80 is de-energized, compression spring 94serves to urge walking beam 28 to rotate about stud 40 in a mannerdefining an open shutter condition. Movement of the plunger and springassembly along the stroke path indicated is permitted by virtue of anopening (not shown) formed within the forward face 42 of bracket 44.

Stud 40, extending from forward face 42 of bracket 44, also serves tosupport a closing spring 100 (FIG. 2). Formed in a multiple turn,helical or spirally wound fashion, spring 100 is slidably mounted aboutstud 42 rearwardly of walking beam 28 and is oriented having its movingend 102 configured to be hooked about a small detent in the upper arm ofwalking beam 28. The stationary end 104 of spring 100 is inserted withina selected detent of a comb-shaped calibrating flange 106. Flange 106 isformed as an upwardly extending rearward side of bracket 44. Bracket 44is connected by a fastener (not shown) to frame or support 86 ofsolenoid 80. Spring 100 is retained upon stud 40 by a connector assemblyincluding a washer 110 and E-ring 112, (FIG. 2).

When mounted, spring 100 is preloaded to a predetermined force value.This loading value is selected to be of a lesser amount than the forcevalues exhibited by compression spring 94. Accordingly, unless solenoid82 is energized to retract plunger 88, the force exerted by closingspring 100 upon walking beam 28, urging blades 24 and 26 into the closedorientation shown in FIG. 3, is overcome and the blades define an openaperture condition as shown in FIGS. 1 and 4. Whensolenoid 82 isenergized, however, plunger 88 compresses spring 94 at a rate selectedto negate the abutting contact of striker surface 90 with pin 96.Accordingly, walking beam 28 and attached blades 24 and 26 are drivensolely by the bias of spring 100 toward the closed terminal positionshown in FIG. 3. This closing motion is ideally consistent and free ofany dynamic influence arising from opening spring 94 or plunger 88. Suchan arrangement advantageously permits consistent performance even thoughthe power supply input of solenoid 80 may vary somewhat. The entiredrive arrangement may be calibrated by adjusting the preloading ofclosing spring 100 at comb-shaped calibrating flange 106. Typically, apredetermined dynamic standard is established and the exposure mechanismis calibrated at 106, accordingly.

Referring additionally to FIG. 5, the characteristics of springs 94 and100 are revealed in more detail. To achieve requisite performance of theexposure mechanism, it is necessary that opening spring 94 be selectedhaving a higher loading characteristic or exhibit higher force valuesthan closing spring 100. As shown in the chart relating relativeposition of blades 24 and 26 with spring loads, opening spring 94operates from a preloaded force value of about 60 grams, when blades 24and 26 are open, to a fully loaded force value of about 70 grams, whenblades 24 and 26 are fully closed. Note additionally, that the loadingcharacteristic of spring 94, in view of its relatively high springindex, is both constant and of a relatively flat rate. The constantcharacteristic permits more consistent design from mechanism tomechanism while the power conserving flat rate characteristic isachieved through selection of aspring index of above about the value-20.

Closing spring 100, being wound by opening spring 94 during-openingmotion of blades 24 and 26, evidences a loaded force value of about 40grams and an unlaoded value of about 25 grams. Spring 100 furtherevidences a relatively flat rate characteristic derived from itsmultiple turn design.

With the spring arrangement shown, blades 24 and 26 of exposuremechanism are driven from a closed orientation towards open positions bythe repeatable or consistent force values of opening spring 94. Indriving walking beam 28 to achieve thisopening, spring 94 is called uponto work against the mass-acceleration characteristics of blades 24 and26, their frictional retardation characteristics as well as the loadingforce values exhibited at closing spring 100. When excitation winding 82of solenoid 80 is energized to terminate an exposure, plunger 88 iswithdrawn or retracted at a rate sufficient to negate the abuttingcontact between striker surface 90 and the striking surface of pin 96,thereby permitting spring 100 to rotate walking beam 28 in a closingdirection. Accordingly, walking beam 28 is driven only from closingspring 100. Inasmuch as spring 100 evidences consistent and repeatableforce values, the closing motion of blades 24 and 26 is ideallyconsistent.

The relatively flat rate selected for springs 94 and 100 advantageouslyreduces the amount of power required of solenoid 80. As evidenced inFIG. 5, a loading value increment (for instance, that in evidencebetween the 40 and 60 gram levels of the graph) is needed in order topermit the loading of spring 100 by spring 94. Through the use of arelatively flat rate and high spring index arrangement, the ultimateload imposed upon solenoid 80 is, disregarding safety factors, about 70grams. Should conventional rate springs be utilized in lieu of the flatrate springs shown at 94 and 100, spring rate curves as at 120 and 122must be considered in the design of the mechanism.

Note thata closing spring of constant higher rate as shown at curve 120would result in a full loading requirement of over 60 grams. A requisiteopening spring rate as shown at curve 122 would commence well above the60 gram position and require a solenoid design having a power outputcharacteristic of much higher levels than those required of the instantmechanism. Where power supplies for the solenoid as at 80 are limited,such loading or power requirements are usually found to be unacceptable.

The structure of the mechanism of the instant invention is particularlyadvantageous where high volume production techniques are contemplated.Note, for instance, that solenoid 80, compression spring 94 and walkingbeam 28 along with supporting bracket 44 can be prefabricated as amodular unit; This unit may then be directly inserted by automatic meansinto rear casting 12. Further, the simplified structure embodied withinthe biased plunger arrangement, is simply fabricated for developing theinitial module. Note additionally, that the entire assembly represents ahighly compact design, a feature of considerable importance for the thincompact housing illustrated.

Since certain changes may be made in the abovedescribed photographicapparatus without departing from the scope of the invention hereininvolved, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings shall be interpretedas illustrative and not in a limiting sense.

What is claimed is:

1. An exposure control mechanism for photographic apparatus comprising:

exposure mechanism means movable toward and away from one position tocontrol the light permitted to pass through an exposure aperture;

tractive electromagnetic means including an excitation winding and amovable armature, said armature being movable in a first direction uponenergization of said excitation winding;

first spring means biasing said exposure mechanism means toward said oneposition; and

second spring means biasing said movable armature in a second directionand effective when said excitation winding is unenergized to cause saidarmature to engage in abuttable contact with and urge said exposuremechanism to move away from said one position against the bias of saidfirst spring means, said armature being moved away from said abuttablecontact upon energization of said winding so as to permit movement ofsaid exposure mechanism means exclusively under the influence of saidfirst spring means.

2. The exposure control mechanism of claim 1 in which:

said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in an orientation selected toprovide said abuttable contact;

said second spring means is present as a compression spring constrainedbetween said supporting means and said armature; and e said first springmeans is configured having a loading characteristic evidencing low ratevalues and instantaneous force values less than corresponding forcevalues exhibited by said second spring means. 3. The 7 exposure controlmechanism of claim 2 wherein said exposure mechanism means is operativeto fully block the said passageof light through said aperture when atthe said one position and is further operative to establish a variationof aperture values over said exposure aperture when moved away from saidone position.

4. An exposure control mechanism for photographic apparatus comprising:

shutter means movable between first and second positions to control thelight permitted to pass through an exposure aperture; tractiveelectromagnetic means including an excitation winding and a movablearmature, said armature being movable in one direction upon excitationof said excitation winding; first spring means biasing said shuttermeans toward said first position and into abutment with said movablearmature; and second spring means biasing said movable armature in asecond direction and effective when said excitation winding isunenergized to force said shutter means into said second positionagainst the bias provided by said first spring means, the energizationof said winding being effective to displace said armature temporarilyout of abutment with said shutter means thereby permitting said firstspring means to move said shutter means to said first position.

5. The exposure control mechanism of claim 4 in which:

said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in an orientation selected toprovide said abuttable contact; and

said second spring means is constrained between said supporting meansand said armature.

6. The exposure control mechanism of claim 4 in which said second springmeans is present as a compression spring.

7. The exposure control mechanism of claim 4 in which:

said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in orientations selected to providesaid abutment; and

said second springmeans is present as a compression spring constrainedbetween said supporting means and said armature.

8. An exposure control mechanism for photographic apparatus comprising:a

valve means selectively movable to block and unblock an exposureaperture;

tractive electromagnetic means including an excitation winding, andarmature means, said armature means being movable in one direction uponenergization of said excitation winding, said tractive electromagneticmeans further including means supporting said excitation winding andsaid armature means in an orientation selected to provide abuttablecontact between said armature means and said valve means;

a compression spring constrained between said supporting means and saidarmature means for urging said armature means to move in one directionestablishing said contact upon de-energization of said excitationwinding;

a second spring having a loading characteristic evidencing low ratevalues and instantaneous force values less than corresponding forcevalues exhibited by said compressing spring and biasing said valve meansfor movement to block said exposure aperture; and

means for adjusting said second spring in a manner pre-loading saidcompression spring so as to calibrate the said movement of said valvemeans to a predetermined standard.

9. The exposure control mechanism of claim 1 in which:

said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in an orientation selected toprovide said abuttable contact; and

said second spring means is constrained between said supporting meansand said armature.

10. The exposure control mechanism of claim 1 in which said secondspring means is present as a compression spring.

11. The exposure control mechanism of claim 1 in which said secondspring means is present as a compression spring having a spring index ofvalue higher than about 20.

12. The exposure control mechanism of claim 1 in which:

said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in orientations selected to providesaid abuttable contact; and

said second spring means is present as a compression spring constrainedbetweensaid supporting means and said armature. v

13. The exposure control mechanism of claim 12 in which said compressionspring is selected having a spring index higher than about 20.

14. The exposure control mechanism of claim 2 in which said secondspring means is present as a compression spring having a spring index ofvalue higher than about 20.

15. The exposure control mechanism of Claim 1 wherein said first springmeans includes means for adjustably preloading said second spring meansso as to calibrate the said movement of said exposure mechanism means toa predetermined standard.

16. The exposure control mechanism of claim 2 wherein said tractiveelectromagnetic means is present as a solenoid, said armature thereofbeing present as a plunger retractable within said excitation windingupon energization thereof and having means defining a striker surface atone end for providing said abuttable contact; and

said compression spring is constrained between said supporting means andsaid means defining a striker surface, so as to spring bias said plungerfor movement outwardly from said excitation winding.

17. The exposure control mechanism of claim 16 in which said exposuremechanism means includes a reciprocally movable striking surfacepositioned for abuttable contact with said striker surface.

18. An exposure control mechanism comprising:

blade means movable in synchronism to block and unblock an exposureaperture;

acutator means reciprocally drivable to move said blade means about saidexposure aperture;

solenoid means having an excitation winding and plunger means saidplunger means being configured having a striker surface abuttablycontactable with said actuator means;

closing spring means cooperating with said actuator means forselectively moving said blade means toward a position effecting theblocking of said exposure aperture;

' opening spring means cooperating with said plunger means for urgingsaid striker surface into said contact with said actuator means toeffect aperture unblocking movement of said blade means.

19. The exposure control mechanism of claim 18 in which:

said solenoid means includes means supporting said excitation windingand said plunger means in an orientation selected to provide saidabuttable contact; and said opening spring means is constrained betweensaid supporting means and said plunger means. 20.- The exposure controlmechanism of claim 19 in which:

said opening spring means is present as a compression Spring. 21. Theexposure control mechanism of claim 19 in Y which:

which:

said opening spring is presentas a compression spring; and

said actuator means is configured having a striking surface drivablycontactable by said striker surface to move said blade means toprogressively unblock said aperture when said excitation winding isdeenergized. 23. The exposure control mechanism of claim 22 in which:

said closing spring means is configured having a loading characteristicevidencing a low rate and instantaneous force values less thancorresponding force values exhibited by said compression spring. 24. Theexposure control mechanism of claim 23 in which:

said solenoid means is configured for retracting said plunger meanswithin said excitation winding upon energization thereof, saidretraction being selected to load said compressin spring at a ratenegating abutting contact between said striker surface and said strikingsurface so as to permit said closing spring to drive said actuator meansto move said blocking position. 25. The exposure control mechanism ofclaim 24 in which:

said compression spring is configured having a spring index value higherthan about 20.

26. The exposure control mechanism of claim 24 wherein said closingspring means includes adjustable preloading means for calibrating thesaid movement of said blade means to a predetermined dynamic standard.

1. An exposure control mechanism for photographic apparatus comprising:exposure mechanism means movable toward and away from one position tocontrol the light permitted to pass through an exposure aperture;tractive electromagnetic means including an excitation winding and amovable armature, said armature being movable in a first direction uponenergization of said excitation winding; first spring means biasing saidexposure mechanism means toward said one position; and second springmeans biasing said movable armature in a second direction and effectivewhen said excitation winding is unenergized to cause said armature toengage in abuttable contact with and urge said exposure mechanism tomove away from said one position against the bias of said first springmeans, said armature being moved away from said abuttable contact uponenergization of Said winding so as to permit movement of said exposuremechanism means exclusively under the influence of said first springmeans.
 2. The exposure control mechanism of claim 1 in which: saidtractive electromagnetic means includes means supporting said excitationwinding and said armature in an orientation selected to provide saidabuttable contact; said second spring means is present as a compressionspring constrained between said supporting means and said armature; andsaid first spring means is configured having a loading characteristicevidencing low rate values and instantaneous force values less thancorresponding force values exhibited by said second spring means.
 3. Theexposure control mechanism of claim 2 wherein said exposure mechanismmeans is operative to fully block the said passage of light through saidaperture when at the said one position and is further operative toestablish a variation of aperture values over said exposure aperturewhen moved away from said one position.
 4. An exposure control mechanismfor photographic apparatus comprising: shutter means movable betweenfirst and second positions to control the light permitted to passthrough an exposure aperture; tractive electromagnetic means includingan excitation winding and a movable armature, said armature beingmovable in one direction upon excitation of said excitation winding;first spring means biasing said shutter means toward said first positionand into abutment with said movable armature; and second spring meansbiasing said movable armature in a second direction and effective whensaid excitation winding is unenergized to force said shutter means intosaid second position against the bias provided by said first springmeans, the energization of said winding being effective to displace saidarmature temporarily out of abutment with said shutter means therebypermitting said first spring means to move said shutter means to saidfirst position.
 5. The exposure control mechanism of claim 4 in which:said tractive electromagnetic means includes means supporting saidexcitation winding and said armature in an orientation selected toprovide said abuttable contact; and said second spring means isconstrained between said supporting means and said armature.
 6. Theexposure control mechanism of claim 4 in which said second spring meansis present as a compression spring.
 7. The exposure control mechanism ofclaim 4 in which: said tractive electromagnetic means includes meanssupporting said excitation winding and said armature in orientationsselected to provide said abutment; and said second spring means ispresent as a compression spring constrained between said supportingmeans and said armature.
 8. An exposure control mechanism forphotographic apparatus comprising: valve means selectively movable toblock and unblock an exposure aperture; tractive electromagnetic meansincluding an excitation winding, and armature means, said armature meansbeing movable in one direction upon energization of said excitationwinding, said tractive electromagnetic means further including meanssupporting said excitation winding and said armature means in anorientation selected to provide abuttable contact between said armaturemeans and said valve means; a compression spring constrained betweensaid supporting means and said armature means for urging said armaturemeans to move in one direction establishing said contact uponde-energization of said excitation winding; a second spring having aloading characteristic evidencing low rate values and instantaneousforce values less than corresponding force values exhibited by saidcompressing spring and biasing said valve means for movement to blocksaid exposure aperture; and means for adjusting said second spring in amanner pre-loading said compression spring so as to calibrate the saidmovement of said valve means to a predetermined standard.
 9. Theexposure control mechanism of claim 1 in which: said tractiveelectromagnetic means includes means supporting said excitation windingand said armature in an orientation selected to provide said abuttablecontact; and said second spring means is constrained between saidsupporting means and said armature.
 10. The exposure control mechanismof claim 1 in which said second spring means is present as a compressionspring.
 11. The exposure control mechanism of claim 1 in which saidsecond spring means is present as a compression spring having a springindex of value higher than about
 20. 12. The exposure control mechanismof claim 1 in which: said tractive electromagnetic means includes meanssupporting said excitation winding and said armature in orientationsselected to provide said abuttable contact; and said second spring meansis present as a compression spring constrained between said supportingmeans and said armature.
 13. The exposure control mechanism of claim 12in which said compression spring is selected having a spring indexhigher than about
 20. 14. The exposure control mechanism of claim 2 inwhich said second spring means is present as a compression spring havinga spring index of value higher than about
 20. 15. The exposure controlmechanism of Claim 1 wherein said first spring means includes means foradjustably preloading said second spring means so as to calibrate thesaid movement of said exposure mechanism means to a predeterminedstandard.
 16. The exposure control mechanism of claim 2 wherein saidtractive electromagnetic means is present as a solenoid, said armaturethereof being present as a plunger retractable within said excitationwinding upon energization thereof and having means defining a strikersurface at one end for providing said abuttable contact; and saidcompression spring is constrained between said supporting means and saidmeans defining a striker surface, so as to spring bias said plunger formovement outwardly from said excitation winding.
 17. The exposurecontrol mechanism of claim 16 in which said exposure mechanism meansincludes a reciprocally movable striking surface positioned forabuttable contact with said striker surface.
 18. An exposure controlmechanism comprising: blade means movable in synchronism to block andunblock an exposure aperture; acutator means reciprocally drivable tomove said blade means about said exposure aperture; solenoid meanshaving an excitation winding and plunger means said plunger means beingconfigured having a striker surface abuttably contactable with saidactuator means; closing spring means cooperating with said actuatormeans for selectively moving said blade means toward a positioneffecting the blocking of said exposure aperture; opening spring meanscooperating with said plunger means for urging said striker surface intosaid contact with said actuator means to effect aperture unblockingmovement of said blade means.
 19. The exposure control mechanism ofclaim 18 in which: said solenoid means includes means supporting saidexcitation winding and said plunger means in an orientation selected toprovide said abuttable contact; and said opening spring means isconstrained between said supporting means and said plunger means. 20.The exposure control mechanism of claim 19 in which: said opening springmeans is present as a compression spring.
 21. The exposure controlmechanism of claim 19 in which: said opening spring means is present ona compression spring having a spring index value higher than about 20.22. The exposure control mechanism of claim 19 in which: said openingspring is present as a compression spring; and said actuator means isconfigured having a striking surface drivably contactable by saidstriker surface to move said blade means to progressively unblock saidaperture when said excitation winding is de-energized.
 23. The exposurecontrol mechanism of claim 22 in which: saId closing spring means isconfigured having a loading characteristic evidencing a low rate andinstantaneous force values less than corresponding force valuesexhibited by said compression spring.
 24. The exposure control mechanismof claim 23 in which: said solenoid means is configured for retractingsaid plunger means within said excitation winding upon energizationthereof, said retraction being selected to load said compressin springat a rate negating abutting contact between said striker surface andsaid striking surface so as to permit said closing spring to drive saidactuator means to move said blocking position.
 25. The exposure controlmechanism of claim 24 in which: said compression spring is configuredhaving a spring index value higher than about
 20. 26. The exposurecontrol mechanism of claim 24 wherein said closing spring means includesadjustable preloading means for calibrating the said movement of saidblade means to a predetermined dynamic standard.